1. Field of the Invention
This invention relates to an image signal transmission apparatus for transmitting image signals produced in a personal computer to a display device, such as a liquid crystal projector, plasma display panel (PDP) or the like, which is relatively remote from the personal computer.
2. Description of the Prior Art
[1] In a case of transmitting image signals produced in a personal computer to a display device via an analog transmission cable, if the analog transmission cable is long, it is apt to cause image deterioration. Such image deterioration will be noticeable especially on the display device having a high resolution of 1024.times.768 pixels (XGA), 1280.times.1024 pixels (SXGA) or the like.
Some image signal transmission apparatus have already been developed that cause no image deterioration even when the transmission cables are long. An example of those apparatus is xe2x80x9cPanelLinkxe2x80x9d by Silicon Image, Inc. in the United States, which has been developed based on a signal transmission technology called TMDS (Transition Minimized Differential Signaling).
According to this signal transmission technology of TMDS, red, blue and green signals (RGB) and a clock signal are serially transmitted in a differential method. This differential method, which is a method for transmitting a single signal by use of two transmission lines, realizes noise immunity and a stable signal transmission and further achieves a high transmission speed and a long-distance cable transmission. It becomes, however, difficult for this method to provide such transmissions if the resolution of image data is further raised up to an ultrahigh resolution of 1600.times.1200 pixels (UXGA), 2048.times.1536 pixels (QXGA) or the like which causes the transmission cable to reach its own physical limit. As a solution to this problem, there has been proposed xe2x80x9cDual Link Methodxe2x80x9d by the DDWG (Digital Display Working Group) in its DVI (Digital Visual Interface) specification. Unlike the conventional xe2x80x9cPanelLinkxe2x80x9d (which will be referred to as xe2x80x9cSingle Linkxe2x80x9d method in contrast to the xe2x80x9cDual Linkxe2x80x9d method hereinafter), the xe2x80x9cDual Linkxe2x80x9d method transmits the R, G, and B signals, by use of not a respective single channel for each signal, that is, three channels but two channels for each signal, that is, six channels, after performing a one-phase to two-phase conversion of each signal. In this way, the xe2x80x9cDual Linkxe2x80x9d method can ensure a bandwidth that is twice as wide as that of the xe2x80x9cSingle Linkxe2x80x9d method, allowing the image transmission of an ultrahigh resolution, such as UXGA, QXGA or the like. Additionally, the one-phase to two-phase conversion of each signal can reduce the required transmission rate and hence realizes the signal transmission through a longer cable.
FIGS. 1 and 2 show the structures of signal transmission apparatus employing the xe2x80x9cSingle Linkxe2x80x9d and xe2x80x9cDual Linkxe2x80x9d methods, respectively.
In the signal transmission apparatus employing the xe2x80x9cSingle Linkxe2x80x9d method, a PanelLink transmitter 301 receives image data represented by parallel signals and performs a parallel-serial conversion of the image data from the parallel signals to serial signals. The image data of serial-converted signals are transmitted through a cable 302 to a PanelLink receiver 303. The cable 302 comprises three pairs of signal lines for transmitting the image data and one pair of signal lines for transmitting a clock signal. The PanelLink receiver 303 performs a serial-parallel conversion of the received serial signals to the parallel signals.
In the signal transmission apparatus employing the xe2x80x9cDual Linkxe2x80x9d method, the even data of image data represented by parallel signals are applied to a PanelLink transmitter 401, while the odd data of the image data are applied to a PanelLink transmitter 402. The PanelLink transmitters 401 and 402 each perform a parallel-serial conversion of the received image data from the parallel signals to serial signals.
The even data of the image data that have been converted into the serial signals by the PanelLink transmitter 401 are transmitted through a cable 403 to a PanelLink receiver 404. The odd data of the image data that have been converted into the serial signals by the PanelLink transmitter 402 are transmitted through the cable 403 to a PanelLink receiver 405. The cable 403 comprises six pairs of signal lines for transmitting the image data and one pair of signal lines for transmitting a clock signal. The PanelLink receivers 404 and 405 each perform a serial-parallel conversion of the received serial signals to the parallel signals.
The object of the present invention is to provide an image signal transmission apparatus that allows the transmission of image signals to be done by use of a transmission method suitable for the resolution of the image signals.
[2] If, in the xe2x80x9cDual Linkxe2x80x9d method of FIG. 2, the RGB image data represented by the parallel signals are not separated into even and odd data but are applied to the PanelLink transmitter 401 as they are, and if the PanelLink receiver 404 only is activated, while the PanelLink transmitter 402 and PanelLink receiver 405 not being activated, then it would correspond to the xe2x80x9cSingle Linkxe2x80x9d method of FIG. 1.
It is difficult for the xe2x80x9cPanelLinkxe2x80x9d method to effect the transmission of an ultrahigh resolution, such as UXGA, QXGA or the like, and/or effect a long-distance transmission. Thus, in the case of effecting such an ultrahigh resolution transmission and/or a long-distance transmission, the xe2x80x9cDual Linkxe2x80x9d method is effective.
On the other hand, in the case of transmitting the signal of a low-resolution, such as VGA or the like, the xe2x80x9cSingle Linkxe2x80x9d method works to a sufficient degree. In addition, because of an increasing demand for portability of the apparatus on the image transmitting side, such as a personal computer or the like, and that on the image receiving side, such as a liquid crystal projector or the like, the need to reduce the power consumption has become important. Thus, when a low-resolution signal is transmitted or when no long-distance transmission is required, it is more desirable to effect the signal transmission by use of the xe2x80x9cSingle Linkxe2x80x9d method.
The object of the present invention is to provide an image signal transmission apparatus that allows the transmission of image signals to be done by use of a transmission method suitable for the resolution of the image signals and for the cable length. [3] In a case of transmitting image signals produced in a personal computer to a liquid crystal projector via an analog transmission cable, if the analog transmission cable is long, it is apt to cause image deterioration. Such image deterioration will be noticeable especially on the liquid crystal projector having a high resolution of 1024.times.768 pixels (XGA), 1280.times.1024 pixels (SXGA) or the like.
There have already been developed some image signal transmission apparatus that can avoid image deterioration even when the transmission cable is long. An example thereof is xe2x80x9cFPDLinkxe2x80x9d developed by National Semiconductor Corp. in the United States. This image signal transmission apparatus is also called xe2x80x9cLVDS.xe2x80x9d
Another example is xe2x80x9cPanelLinkxe2x80x9d by Silicon Image, Inc. in the United States.
FIG. 3 shows the structure of xe2x80x9cPanelLink,xe2x80x9d which comprises a graphics controller (graphics board) 151 built in a personal computer, a transmitting-side unit 152, a receiving-side unit 153, and a cable 154 for connecting the transmitting-side unit 152 and the receiving-side unit 153.
The transmitting-side unit 152 includes an encoding/parallel-serial converting circuit 161, a PLL circuit 162, and an amplitude control circuit 163. The encoding/parallel-serial converting circuit 161 receives image data, DE (i.e., a display enable signal for discriminating between a display mode and a standby mode), and a control signal from the graphics controller 151.
In the encoding/parallel-serial converting circuit 161, a parallel-serial conversion of the 24-bit parallel image data is performed, whereby the number of signal lines can be reduced and hence the signal transmission can be effected through a thin cable. Then, the signal amplitude is reduced so as to reduce EMI noise. Additionally, the encoding is performed at the time of the parallel-serial conversion. When the encoding is performed, the variation of the level of the signals to be transmitted is reduced so as to further reduce the EMI noise.
The PLL circuit 162 generates a clock signal for the encoding/parallel-serial converting circuit 161 on the basis of a clock signal applied from the graphics controller 151.
The cable 154 comprises three pairs of signal lines for transmitting the codes including the image data and the control signal, and one pair of signal lines for transmitting the clock signal generated by the PLL circuit 162.
The amplitude control circuit 163 adjusts, in accordance with the resistance value of a single external resistor 165, the amplitude of the signals (i.e., the codes including the image data and the control signal, and the clock signal) to be applied from the transmitting-side unit 152 to the cable 154. Specifically, the signal amplitude can be adjusted within a range between 0.5 V and 2.5 V by establishing the resistance value of the single external resistor 165.
The receiving-side unit 153 includes a data extracting/serial-parallel converting/decoding circuit 181 and a PLL circuit 182. The data extracting/serial-parallel converting/decoding circuit 181 performs a data extraction, a serial-parallel conversion and a decoding with respect to the codes applied from the transmitting-side unit 152 to produce the image data, DE and the control signal.
The PLL circuit 182 produces a clock signal for the data extracting/serial-parallel converting/decoding circuit 181 on the basis of the clock signal applied from the transmitting-side unit 152.
The image data, DE and control signal produced by the data extracting/serial-parallel converting/decoding circuit 181 and the clock signal produced by the PLL circuit 182 are applied to a liquid crystal panel 155 of digital drive type.
The xe2x80x9cLVDSxe2x80x9d method is similar to the xe2x80x9cPanelLinkxe2x80x9d method but different therefrom in that the total number of the signal lines in the cable is five because of performing neither encoding nor decoding.
FIG. 4 shows the structure of an image signal transmission apparatus that has already been developed by the Applicant of the subject application (See Japanese Official Gazette of Laid Open Patent Application, TOKUKAI, No. 2000-341177.) In FIG. 4, elements corresponding to the same elements in FIG. 3 are identified by the same reference designations, and the explanation of those elements is omitted.
The image signal transmission apparatus of FIG. 4, which utilizes the conventional xe2x80x9cPanelLinkxe2x80x9d, comprises a transmission unit 10 set in a personal computer (which is not shown and which will be referred to as xe2x80x9cPCxe2x80x9d hereinafter) 1, a receiving-side unit 153 set in a liquid crystal projector 20, and a cable 154 for connecting the transmission unit 10 and the receiving-side unit 153.
The transmission unit 10 comprises a graphics controller (graphics board) 151 and a transmitting-side unit 152 connected thereto. The graphics controller 151 is connected to a main CPU 2 in the PC 1 via a bus 3 also therein. The transmitting-side unit 152 in the transmission unit 10 is connected to the receiving-side unit 153 via the cable 154.
The receiving-side unit 153 in the liquid crystal projector 20 is connected to a liquid crystal panel 155 of digital drive type also in the liquid crystal projector 20.
An amplitude control circuit 163 adjusts, in accordance with the resistance value of an external variable resistor circuit 164, the amplitude of the signals (i.e., the codes including the image data and the control signal, and the clock signal) to be provided from the transmitting-side unit 152 to the cable 154. The variable resistor circuit 164 can be switched, for example, between two resistance values to thereby switch, between two values, the amplitude of the signals to be provided from the transmitting-side unit 152 to the cable 154.
An application software for setting the cable length has been installed on the PC 1. When setting the cable length, the user initiates this application software. When this application software is initiated, the PC 1 produces, on its display device, an on-screen selection guide for instructing the user to designate the length of the cable 154 actually being used. The user selects a cable length, following the on-screen selection guide.
When the user selects the cable length, the PC 1 sends a command signal (amplitude command signal) responsive to the cable length selected by the user to the graphics controller 151 via the bus 3. Receiving this command signal, the graphics controller 151 sends an amplitude control signal responsive to the command signal to the variable resistor circuit 164 to change the resistance value thereof.
According to the image signal transmission apparatus of FIG. 4, the user can adjust, in accordance with the cable length, the amplitude of the signals to be provided from the transmitting-side unit 152 to the cable 154 by operating the PC 1 in which the graphics controller 151 has been disposed.
Meanwhile, in the image signal transmission apparatus of the xe2x80x9cLVDSxe2x80x9d or xe2x80x9cPanelLinkxe2x80x9d method, if the amplitude of signals to be transmitted is enlarged, it increases the possible distance of transmission by the cable but also increases unwanted radiation signals. In contrast to this, if the amplitude of signals to be transmitted is reduced, it reduces the unwanted radiation signals but also reduces the possible transmission distance.
Thus, it is desirable to optimize the signal amplitude according to the cable length. The xe2x80x9cLVDSxe2x80x9d method, however, has no function to adjust the signal amplitude. As described above, the xe2x80x9cPanelLinkxe2x80x9d method indeed has the function to adjust the signal amplitude by use of the single external resistor 165. However, since the external resistor 165 is disposed at the stage of design, it is difficult for the user to adjust the signal amplitude according to the cable length.
Additionally, in the case of the image signal transmission apparatus of FIG. 4, it was necessary for the user to enter into the PC 1 the amplitude control command for changing the amplitudes of the signals to be provided from the transmitting-side unit to the cable, according to the cable length.
It was, therefore, necessary to preinstall the cable length setting application software onto the PC 1. Additionally, at the time of setting the cable length, it was necessary for the user to initiate this cable length setting application software to cause the on-screen selection guide for setting the cable length to be displayed on the PC 1, and then select the cable length, following this on-screen selection guide.
Moreover, each time changing a cable for another having a different length, the user had to enter an amplitude control command into the computer.
The object of the present invention is to provide an image signal transmission apparatus that does not necessitate the user""s setting of the cable length but automatically adjusts the amplitude of signals to be applied from the image transmitting-side unit in response to the level of the received signals that varies with the cable length.
A first image signal transmission apparatus according to the present invention performs a parallel-serial conversion of parallel image data by use of an image-transmitting-side device, thereafter transmits the image data to an image-receiving-side device via a cable, and then performs a serial-parallel conversion of the received image data by use of the image-receiving-side device, said image-transmitting-side device comprising: a one-phase to two-phase converter circuit for separating the parallel image data, which are to be transmitted, into even and odd data; a first parallel-serial converting circuit; a second parallel-serial converting circuit; means for allowing a user to select, as the resolution mode for the image data to be transmitted, one of a first resolution mode and a second resolution mode that is higher in resolution than the first resolution mode; and switch means for applying the parallel image data, which are to be transmitted, to the first parallel-serial converting circuit when the first resolution mode is selected, and for applying the parallel image data, which are to be transmitted, to the one-phase to two-phase converter circuit when the second resolution mode is selected; wherein when the second resolution mode is selected, the even data obtained by the one-phase to two-phase converter circuit are applied to one of the first and second parallel-serial converting circuits, and the odd data obtained by the one-phase to two-phase converter circuit are applied to the other parallel-serial converting circuit.
A second image signal transmission apparatus according to the present invention performs a parallel-serial conversion of parallel image data by use of an image-transmitting-side device, thereafter transmits the image data to an image-receiving-side device via a cable, and then performs a serial-parallel conversion of the received image data by use of the image-receiving-side device, said image-transmitting-side device comprising: a one-phase to two-phase converter circuit for separating the parallel image data, which are to be transmitted, into even and odd data; a first parallel-serial converting circuit; a second parallel-serial converting circuit; means for automatically determining the resolution of the image data to be transmitted, and then automatically selecting, as the resolution mode for the image data to be transmitted, one of a first resolution mode and a second resolution mode that is higher in resolution than the first resolution mode; and switch means for applying the parallel image data, which are to be transmitted, to the first parallel-serial converting circuit when the first resolution mode is selected, and for applying the parallel image data, which are to be transmitted, to the one-phase to two-phase converter circuit when the second resolution mode is selected; wherein when the second resolution mode is selected, the even data obtained by the one-phase to two-phase converter circuit are applied to one of the first and second parallel-serial converting circuits, and the odd data obtained by the one-phase to two-phase converter circuit are applied to the other parallel-serial converting circuit.
In the above-described first or second image signal transmission apparatus, said image-receiving-side device comprises: a first serial-parallel converting circuit for converting the serial data, transmitted from the first parallel-serial converting circuit via the cable, to the parallel data; and a second serial-parallel converting circuit for converting the serial data, transmitted from the second parallel-serial converting circuit via the cable, to the parallel data.
The above-described first serial-parallel converting circuit includes means for performing a one-phase to two-phase conversion of the parallel data obtained by the serial-parallel conversion to provide separated even and odd data in the case when the first resolution mode is selected.
A third image signal transmission apparatus according to the present invention performs a parallel-serial conversion of parallel image data by use of an image-transmitting-side device, thereafter transmits the image data to an image-receiving-side device via a cable, and then performs a serial-parallel conversion of the received image data by use of the image-receiving-side device,
said image-receiving-side device comprising: means for detecting the level of the signals transmitted from the image-transmitting-side device through the cable to the image-receiving-side device and for generating an operation mode control signal for designating a first operation mode when the detected signal level is higher than a predetermined value and for designating a second operation mode when the detected signal level is equal to or lower than the predetermined value; and means for transmitting the operation mode control signal to the image-transmitting-side device,
said image-transmitting-side device comprising: a one-phase to two-phase converter circuit for separating the parallel image data, which are to be transmitted, into even and odd data; a first parallel-serial converting circuit; a second parallel-serial converting circuit; and switch means for applying the parallel image data, which are to be transmitted, to the first parallel-serial converting circuit when the operation mode control signal from the image-receiving-side device designates the first operation mode, and for applying the parallel image data, which are to be transmitted, to the one-phase to two-phase converter circuit when the operation mode control signal from the image-receiving-side device designates the second operation mode,
wherein when the operation mode control signal from the image-receiving-side device designates the second operation mode, the even data obtained by the one-phase to two-phase converter circuit are applied to one of the first and second parallel-serial converting circuits, and the odd data obtained by the one-phase to two-phase converter circuit are applied to the other parallel-serial converting circuit.
In the above-described third image signal transmission apparatus, said image-receiving-side device comprises: a first serial-parallel converting circuit for converting the serial data, transmitted from the first parallel-serial converting circuit via the cable, to the parallel data; and a second serial-parallel converting circuit for converting the serial data, transmitted from the second parallel-serial converting circuit via the cable, to the parallel data.
The above-described first serial-parallel converting circuit includes means for performing a one-phase to two-phase conversion of the parallel data obtained by the serial-parallel conversion to provide separated even and odd data in the case when the first operation mode is selected.
The above-described means for transmitting the operation mode control signal to the image-transmitting-side device may transmit the operation mode control signal by wire or by wireless.
A fourth image signal transmission apparatus according to the present invention comprises comprising an image-transmitting-side device, an image-receiving-side device, and a cable connecting the image-transmitting-side device with the image-receiving-side device,
said image-receiving-side device comprising: means for detecting the level of the signals transmitted from the image-transmitting-side device through the cable to the image-receiving-side device and for generating, in accordance with the detected signal level, a control signal for controlling the amplitude of the signals to be applied from the image-transmitting-side device to the cable; and means for transmitting the control signal to the image-transmitting-side device,
said image-transmitting-side device having amplitude control means for controlling, in accordance with the control signal from the image-receiving-side device, the amplitude of the signals to be applied from the image-transmitting-side device to the cable.
In the above-described fourth image signal transmission apparatus, said amplitude control means may comprise: for example, an amplitude control circuit for changing, in accordance with the resistance value of an external amplitude control resistor, the amplitude of the signals to be applied from the image-transmitting-side device to the cable; a variable resistor circuit disposed, as the amplitude control resistor, externally to the amplitude control circuit; and means for controlling the resistance value of the variable resistor circuit in accordance with the control signal from the image-receiving-side device.
The above-described means for transmitting the control signal to the image-transmitting-side device may transmit the control signal by wire or by wireless.